Dr. Edmond I. Eger II, a leader in the development of a now universally used technique to determine the proper dose of anesthetic gas administered in operating rooms — an advance that has saved an untold number of lives — died on Aug. 26 at his home in Tiburon, Calif. He was 86.

The cause was pancreatic cancer, said Dr. Steven L. Shafer, a professor of anesthesiology, perioperative and pain medicine at Stanford University, and the editor of a coming autobiography of Dr. Eger.

Inhaled gases like ether and chloroform had been in use as anesthetics for more than 100 years when Dr. Eger graduated from medical school in 1955, but there was still no clear standard for dosing, or for comparing the strength of one gas to another.

Without a systematic way to measure the effects of anesthesia, doctors looked for signs like changes in a patient’s muscle tone, breathing and pupil diameter. But those traits were of no use in research because they varied from patient to patient and did not occur in lab animals. As new anesthetic gases were developed, the need grew for a more precise way to test, compare and dose them.

Dr. Eger devised a method working with Dr. Giles Merkel, Dr. Lawrence Saidman and other anesthesiologists at the University of California, San Francisco. They identified one value to use as a benchmark: the concentration of anesthesia at which 50 percent of patients did not move in response to a painful stimulus, like being cut with a scalpel.

Other patients would require a slightly higher or lower concentration to achieve the same effect, but the variations were not large.

That led to their introduction in 1965 of a concept, called the minimum alveolar concentration, or MAC, that quickly became the standard measure of potency for anesthetic gases.

Because powerful anesthetics work at lower concentrations and weaker ones require higher doses, a lower MAC value would indicate a stronger drug. Anesthesiologists use MAC values when planning doses needed for surgery.

The values are highly consistent from one patient to another and even among animals. For any given drug, about the same concentration can anesthetize a 200-pound man, a smaller woman, a dog or a rat. The amount needed to reach that concentration differs depending on the patient’s size, but the effective concentration itself does not change.

Dr. Shafer said the technique devised by Dr. Eger and his colleagues made the administering of anesthesia far safer and has saved millions of lives.

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Dr. Eger in an undated photograph.CreditRichard Schlobohm

In later work, Dr. Eger identified new drugs that could be used as anesthesia, such as isoflurane, sevoflurane and desflurane, which are still the most widely used general anesthetics.

“Ted Eger revolutionized modern anesthetic practice, and led the way to the development of the anesthetic gases used tens of millions of times a year,” Dr. Michael A. Gropper, the chairman of the department of anesthesia and perioperative care at the University of California, San Francisco, wrote in an email.

Edmond I. Eger II was born on Sept. 3, 1930, in Chicago. (His parents gave him a middle initial but not a middle name.) His father was an advertising executive, and his mother, the former Miriam Newmann, was a homemaker.

As a boy, Dr. Eger skipped at least one grade, became a whiz at checkers and led the Hyde Park High School checker team to two city championships. He graduated at 15, but, as a bored and indifferent student, wound up in the bottom 20 percent of the class.

He was soon hired to sell women’s shoes, but after only one day on the job he decided he had had enough and resolved to apply for college. He was accepted at Roosevelt College in Chicago, where “he went from not working at all to working his butt off,” Dr. Shafer said.

After a year, he transferred to the University of Illinois, where he majored in chemistry with a minor in math. He went to medical school at Northwestern University.

In 1955, the same year he graduated from Northwestern, he married Dollie Ross, a speech therapist. The marriage ended in divorce in 1983. In 1996, he married Dr. Lynn Spitler, an immunologist, who survives him.

Dr. Eger is also survived by three daughters, Cris Cadence Waste, Doreen J. Eger and Renee R. Eger, and a son, Edmond Eger III, all from his first marriage; a half brother, Larry Eger; two stepchildren; seven grandchildren; and six step-grandchildren.

After completing his internship and residency, Dr. Eger served for two years as a captain in the medical corps, based at the Army hospital at Fort Leavenworth, Kan. From 1960 to 2006 he was a faculty member at the University of California, San Francisco. He was an author of more than 500 scientific articles and an author or editor of seven books.

“He received every award known to man in his specialty,” Dr. Shafer said.

Dr. Eger spent the last 20 years of his career trying to understand how inhaled anesthetics work. The drugs and their effects remain a mystery. The same concentration that knocks out a person will anesthetize a sea slug or an amoeba, and will even paralyze a fern that normally curls up when touched, Dr. Shafer said. The universality of those reactions suggests that the drugs are tapping into some biological mechanism that evolved eons ago.

Dr. Eger regretted that he had not been able to discover that mechanism, writing in his autobiography, “The ‘ah ha!’ moment, the thrill of solving the hardest puzzle in all of pharmacology, awaits another investigator.”

A version of this article appears in print on , on Page A24 of the New York edition with the headline: Dr. Edmond Eger II, 86; Developed Benchmark For Anesthesia Dosage. Order Reprints | Today’s Paper | Subscribe